Technical Field
The present invention relates to a method for analyzing images generated from at least one imaging system on at least one satellite, a method for image correction, a method for providing a three-dimensional image, a method for generating a 3D model of the environment, a computer program, a computer program product and a system for performing any of the methods.
Related Art
When images are taken by an imaging system on a satellite it is desirable to get as accurate images as possible, i.e. the final images should give a picture of the area or scenery which is as close to reality as possible. This could, for example, be that geometric shapes on the ground correspond to the same geometric shapes in the image, or that distances between objects in the image correspond to the distance in reality. For achieving this, usually some correction of the images provided by the imaging system is needed. This correction can be performed either in the imaging system at the satellite or in the images at any later stage, for example by computers on the ground.
One of the reasons why corrections are needed is that internal and/or external parameters of the imaging system might change over time, for example, due to the rough conditions when launching the satellite, due to degradations in the system, due to temperature changes, and/or due to imperfections in measuring or controlling devices. This might, for example, affect lenses, sensors or any other equipment onboard the satellite.
In some satellites, sensors are staggered and might partially overlap. Then some image processing is needed to compensate for the different positions of the sensors and to provide one image out of the signals received by the several sensors. This image processing, among other things, takes care of the relative position and of the relative orientations of the sensors. Also the relative position and the relative orientation of the sensors can change over time.
Another reason for the need of corrections are imperfections in external data used to rectify raw data of a satellite. This can, for example, be imperfections in an elevation model used to combine data from staggered sensors to arrive at a provided image from a satellite.
Due to weight, space and/or power constraints on satellites it is often not practical to add extra equipment on satellites for monitoring changes of sensors or parameters in imaging systems. Instead, one usually first builds a model of how different changes of parameters or components of the imaging system influence images provided by the imaging system. Then, for example, images are taken by the imaging system of areas where so-called ground control points (GCP) are known or could be measured via surveying, and an equation system will be solved where GCP enter as known quantities, so that after solving of the equation system GCP in the imaging correspond as close as possible to the respective position of the GCP in reality. The equation system will then provide new values for parameters of the imaging system and/or for the orientation and relative position of sensors or other components therein. These new parameters can then be used in imaging processing/correction of further images.